1. Field of the Invention
The present invention relates generally to Raman spectroscopy, and more particularly to methods for obtaining enhanced Raman spectra signal intensity from thin film contaminants on a substrate surface.
2. Description of the Prior Art
Unwanted contamination on the surface of a substrate can adversely affect operational and manufacturing processes that depend upon a clean substrate surface. For instance, where unwanted contamination is disposed on a hard disk surface, or on the surface of a read/write head, the signal to noise ratio (S/N) can be adversely affected, and where the surface contamination is particularly severe, a head crash can occur which can destroy a hard disk drive. Given the continually shrinking head/disk interface tolerances, contamination by thin films of nanometer level thickness can create substantial problems; such contaminating thin films are termed smears and often are the result of contamination during one or more steps in the disk or head manufacturing process or handling subsequent to manufacturing. Many of such smears are comprised of organic polymers that exist on the surface of a manufactured hard disk.
A typical smear contamination problem arises during the read/write testing or use of a completed hard disk, where the smear causes a significant signal loss in the contaminated area. It is then important to analyze the smear to determine its composition, because it is often possible to then identify the manufacturing or handling step in which the contamination occurred and thereafter take steps to eliminate the source of the contamination. The throughput of acceptable product can therefore be improved.
A standard technique for the analysis of smears is Raman spectroscopy through which the smear composition can be determined. However, a limitation on the use of standard Raman spectroscopy is the need for a sample that has sufficient thickness to create a scattered signal with sufficient intensity for detection above the background noise. Significantly, where a smear on a hard disk has a thickness on the order of approximately several nanometers or more, it will cause substantial signal degradation; however, the smear thickness is oftentimes insufficient to provide a detectable signal for standard Raman spectrographic analysis. A problem therefore exists in the analysis of thin film smears in order to identify them and thereafter improve manufacturing throughput.
Techniques for surface enhanced Raman spectroscopy exist in the prior art. Such techniques involve the utilization of a metal surface on which a thin film smear is disposed. Where the laser irradiates the smear an enhanced Raman scattering signal is generated. This technique, termed surface enhanced Raman spectroscopy (SERS) is utilizable where the smear is disposed upon a metal substrate, such that the smear is directly irradiated by the laser. However, where the smear is already disposed upon a substrate, such as a hard disk surface, it is not possible to place the smear upon a metal substrate surface, such that the smear can be irradiated by the spectroscopic laser.
A need therefore exists for a method for the analysis of thin film smears that are disposed upon a substrate surface, and particularly a method for obtaining an enhanced Raman scattering spectra signal.